Another day, another set of revelations about antisemitism in the Labour Party. Three of them so far today.

Then at PMQs David Cameron was given an open goal by a question from Finchley MP Mike Freer, asking if he agreed that all organisations “should root out anti-Semitism without hesitation” .

You didn’t have to be Nostradamus to realise where this was heading – and sure enough the PM responded by going for Labour: “We do see a growth in support for segregation and, indeed, for anti-Semitism in parts of the Labour party and I say to the leader opposite, it's his party and he should sort it out."

Yes, it’s using antisemitism to score a political point. But instead of worrying about that, how about worrying about the antisemitism itself? If Labour wasn’t so – to put it charitably – lackadaisical at dealing with the antisemites it is harbouring, there would be no open political goal for David Cameron to shoot at.

Every party has its racists. But can you imagine if some of those Labour members exposed over the past few weeks had been found in the Conservative Party or even UKIP? We would never have heard the end of it from Labour, and how it showed them to be deeply racist.

But there’s a real issue here, because if there had been no media furore then the likes of Gerry Downing and Vicki Kirby would still be Labour members.

So why is Labour so attractive to Jew haters? My theory is that under Mr Corbyn, the party defines itself above all else by “anti-imperialism”, as they call it. And if your politics are anti-imperialist, nothing else matters. So Mr Corbyn happily describes Hamas and Hezbollah representatives as “friends”, despite their penchant for murdering Jews (as well, of course, as Muslims, and everyone else). And with the party leader openly – proudly - alongside these people, anti-Semites swarm to Labour, assured of a warm welcome from their fellow anti-imperialists. So when Mr Cameron says Jeremy Corbyn should “sort it out”, of course he is right. But the chances of that happening are close to zero.